That's understandable, although really pretty unfortunate in the sense that they could've done so much better with regards to openness -- it's hackable, but at the same time, third-party apps still stay very much second-class. Had they made it fully open, and defined proper protocols, extension points and ways to install things without requiring poorly-documented changes in five different places (like when you install CoolReader), it could've combatted a lot of the ecosystem disadvantage they have compared to Kindle and other products offered by companies with huge platforms to back them with.